U.S. Pat. No. 4,836,499 shows a butterfly valve with a shaft sealing member located in the inflatable seal and, more specifically, around the portion of shaft of the butterfly valve extending through the resilient portion of the inflatable seal that forms an interface between the transport line and the inflation chamber of the inflatable seal. Tyically, butterfly valves are used to open or close lines that transport fluids that may contain liquids and or solids. One of the features of most butterfly valves is that the shaft, which extends through the inflatable seal, must be statically and dynamically sealed against the side walls of an opening extending through the resilient portion of the inflatable seal to prevent fluids from escaping therepast. This sealing is more critical if the transport system is to handle liquids and the like that remain under pressure whether the butterfly valve is open or closed. One of the difficulties in making an effective static and dynamic chamber seal is that the physical integrity of the sealing member around the shaft should be maintained or the effectiveness of the inflatable seal may be compromised. Unless the static and dynamic shaft seal is effective one cannot prevent the fluids being transported from contaminating the fluids used to inflate the seal as well as prevent the fluids used to inflate the seals from contaminating the transported fluids. This problem is particularly acute if the fluid transport lines remains pressurized when the butterfly valve inflatable seal is deflated since without an effective shaft seal the pressurized transport fluids leaks out along the shaft and into the inflation chamber of the inflatable seal.
Thus one of the problems in sealing the transport lines from the inflation chamber of the inflatable valves is that the shaft-sealing member is located around the shaft of a butterfly valve that extends through a resilient member that forms part of an inflatable seal which expands and contracts in response to pressurization of the inflatable seal. The two-way static and dynamic shaft-sealing member must be such that the liquid pressures from the transport line cannot force fluid out of the transport line and into the inflation chamber of the inflatable seal nor can the pressures used to inflate the inflatable seal force fluids from the inflation chamber into the transport line. In addition the two-way sealing relationship of the shaft-sealing member to the shaft must be maintained under both static conditions and dynamic conditions that occurs as the shaft rotates from one location to another within the opening extending through the inflatable seal. In addition the shaft-sealing member must also maintain its sealing relationship to the shaft as the shaft-sealing member slides axially along the shaft in response to pressure changes occurring during opening and closing of the butterfly valve. U.S. Pat. No. 4,836,499 patent shows a shaft sealing member located in the massive portion of the inflatable seal comprising a series of circular ridges and grooves. If fluid transport pressure is high the series of ridges and grooves do not prevent liquids from passing through the ridges and grooves when the inflatable seal is in a deflated condition. U.S. Pat. No. 4,836,499 also shows a liquid sealing member for sealing the portion of the inflatable seal behind the inflation chamber with the seal comprising two annular seals that have legs with the legs of the seals located parallel to the axis of the shaft and facing in opposite directions with the annular seals radially held in position by an annular band located in the inflatable seal.
Generally, inflatable seals for valves and more particularly inflatable seals for butterfly valves are well known in the art. To be effective in sealing the transport lines the inflatable seals should be durable for use in abrasive environment and should not contain recesses that become contaminated with the particles being transferred thus requiring periodic flushing of the valve.
The contamination problem is particularly troublesome if food materials are being transported since the accumulated food particles can contaminate the food and produce health risks. A butterfly valve inflatable seal should provide an effective seal around the periphery of the butterfly disk and still provide a valve that can be easily opened or closed. While inflatable seals have eliminated shaft sealing problems by having the axis of rotation of the valve offset from the valve seal, it has been found that such offset valves are prone to accumulation of material along the edges of the valve which may produce contamination in the system. Furthermore, valves with the axis of rotation offset from the seal provide for difficulty in opening or closing since the forces of the material acting on the valve surface create force imbalances making it difficult to oftentimes open and close the valve. In addition, such offset valves do not provide for equal flow since they provide a high profile that oftentimes interferes with the flow of material through the valve. Furthermore, such valves are often bulky and not suitable for use in high pressure large diameter material transportation systems. The present invention provides an improved two-way static and dynamic shaft seal that retains the physical integrity of the inflatable seal while being carried by the resilient portion of the inflatable seal that forms an interface between the transported fluids and the fluids used to pressurize the inflatable seal.